The present invention relates to suspension polymerized copolymers of an alkyl vinyl monomer with styrene and to rubber-modified impact-resistant compostions comprised thereof; more particularly, to a copolymer of a monomeric higher alkyl vinyl compound and styrene graft polymerized under suspension polymerization conditions with a pure preformed rubber; and, to the method for preparing these products by suspension polymerization.
According to the present invention, in a first aspect, it is found that styrene having its polymeric backbone modified as a copolymer with a minor quantity, less than about 15%, of a monomeric alkyl vinyl compound has a built-in lubricating effect, superior in easy-flow molding to more perfect castings at lower molding pressures. The copolymer exhibits better stability of its lubricating properties in storage, being resistant to variations which occur over long storage periods and constitute a common fault of crystal polystyrene particles which have been blended with extraneously added lubricants for molding. It is found moreover that this copolymer comprising the monomeric higher alkyl vinyl compound will expand with a foaming agent to a foam with smaller cells, a substantial advantage over many foamed products formed from expandable polystyrene.
In a second aspect, the invention pertains to copolymers of a higher alkyl vinyl and styrene formed by suspension polymerization in the presence of preformed rubber particles, whereby the copolymer graft polymerizes to the rubber, forming superior high impact copolymer beads, which are easily moldable, with good flow characteristics, as well as of superior impact resistance.